1. You pretty much answered this first one yourself. Let It Be was recorded first, but shelved for a year. Abbey Road was the last album RECORDED, but Let It Be was the last one RELEASED.

2. Someone else may know for sure, but as far as I know, MMT was only released first as a soundtrack recording. (Only with the 6 or however many songs that were played in the film.) Then I think it was later released (maybe only in the US) with the rest of the tracks (Hello Goodbye through All You Need Is Love) to make it a full album. However, maybe it was released as this "full album version" originally in the US to begin with. Am I making sense?

3. I don't consider Yellow Submarine a "studio album" at all. Just a soundtrack to accompany the film.

As for MMT, Capitol records refused to release the material (what we no know as the first 6 tracks) on EP, which was a popular format in Great Britain. It had the songs from MMT, Capitol released those, of course, with the backlog of 1967 singles and one B side (baby you're a rich man) from the band. Strawberry and Penny were originally intended for Pepper and were considered double A sides.

For those who want to consider LIB the last Beatle album can consider this to back their argument. At the time of the AB release (Sept'69) the unreleased "Get Back" tapes that eventually became the LIB album were only about 75% complete. "I Me Mine" was recorded from scratch Jan 3 1970, "Let It Be" the song had numerous overdubs done on Jan 4 (lead gtr.,backup harmonies,brass score,maracas, drum overdubs), "For You Blue" according to some sources state that George's lead vocal was re-done in late Jan, Phil "the murderer?"Spector extended the length of "I Me Mine" about twice, remixed and edited all tracks sometime in March, added orchestral overdubs to "Across The Universe", "The Long And Windy Road" and "I Me Mine" on April 1st with Ringo adding additional drums to TLAWR during that session.

So some might say that considering LIB wasn't quite complete at the time the other supposed last album came out that LIB could be (if one wants to be technical) the last album.